#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
int main()
{
    int i = 0;
    int n = 0;
    int num = 0;
    int sum = 0;
    scanf("%d", &n);
    for (i = 0; i < n; i++)
    {
        scanf("%d", &num);
        sum ^= num;
    }
    printf("%d", sum);
    return  0;
}